Electroluminescent lamp



1 1961 c. M. BROWNE 2,967,964

ELECTROLUMINESCENT LAMP Filed Jun 8, 1956 14 INVENTOR.

@zwclaLW]. l /cowne BY 5 fladefdwope A TTORNE YS Unite States Patent ELECTROLUMINESCENT LAMP Charles M. Browne, Toledo, Ohio, assignor to Libbey- Owens-Ford Glass Company, Toledo, Ohio, :1 corporation of Ohio Filed June 8, 1956, Ser. No. 590,130

'1 Claim. (Cl. 313-108) The present invention relates broadly to electroluminescent lighting, and more particularly to a novel type of electroluminescent lamp having a generally conventional lamp structure and which can be used with conventional electrical outlets.

Electroluminescence is a relatively new type of lighting in which the .light is obtained by direct application of voltage across a phosphor, or by placing the phosphor in an electric field. Lamps for'producing such light are now known, and a representative form of electroluminescent lamp is described in United States Patent No. 2,556,349, issued September 4, 1951, to Eric L. Mager.

However, most of these structures have a number of disadvantages because of their inability to fit conventional sockets, various problems in electric lead wire attachment. and in the exposure of electrically conducting surfaces where a source of electrical shock is available. Accordingly, it is a primary object of this invention to provide an electroluminescent lamp structure which overcomes the above mentioned difiiculties and which is a comparatively simple, practical structure.

Other objects and advantages of the invention will become more apparent during the course of the following description when taken in connection with the accompanying drawings.

In the drawings, wherein like numerals are employed to designate like parts throughout the same:

Fig. 1 is a perspective view of one representative form of the electroluminescent lamp of this invention;

Fig. 2 is an enlarged fragmentary sectional view of the lamp of Fig. 1 illustrating the manner in which the electrically conducting films and phosphor material are disposed within the electroluminescent lamp;

Fig. 3 is a fragmentary view illustrating the attachment of one electrode; and

Fig. 4 is a sectional view of an apparatus illustrating one method of applying an electrically conducting film to the lamp of this invention by a thermal evaporation technique.

The electroluminescent lamp shown in Fig. 1 comprises a cylindrically shaped body 11 and a conventional screw type electrical base 12. The body portion 11 includes a glass tube or cylinder 13 which may be a right circular cylinder as illustrated in the drawing or which may be irregularly or bulb shaped. In the structure illustrated in the drawing, the glass cylinder 13 has a transparent, electrically conducting film 14 attached to the inner surface thereof. On the inner surface of the electrically conducting film 14, there is a layer 15 of dielectric material having an electric field-responsive phosphor imbedded therein. Any solid dielectric material may be used and plastic materials are preferred because of their high dielectric constant. An example of a plastic suitable for the purposes of this invention is plasticized nitrocellulose. Any material that will emit light under the influence of an electric field may be used such as 'a zinc sulfide phosphor, zinc cadmium sulfide, or cadmium sulfide activated with copper or praseodymium. Disposed on the inner surface of the dielectric material is a second electrically conducting film 16 which may or may not be transparent.

In the embodiment illustrated in the drawing, the glass cylinder 13 has a bead 17 which provides engagement of the attachment member 18 which in turn provides a mechanical attachment for the body member 11 and the conventional base 12.

The glass cylinder 13 also has electrodes 19 and 20 which are preferably tabs of fired-on silver. The electrode 19 is in electrical contact with the electrically conducting film 14, while the electrode 20 is in electrical contact with the electrically conducting film 16. Wire 21 is electrically connected to electrode 18 by solder or other means, and is also connected to the electrode 22 of the conventional screw type base 12. Another wire 23 is electrically connected to electrode 20 by solder or other means, and also connected to the jacket 24 and the base 12.

Accordingly, when the lamp 10 is screwed into the conventional electrical outlet and the current is turned on, it is seen that a potential is applied to the electrically conducting films 14 and 16 which causes the field-responsive phosphor disposed therebetween to emit light. Also it is to be noted that the glass cylinder 13 serves as an insulator, completely enclosing the electrically conducting films 14 and 16 and the connections therefor so that this structure is prevented from becoming an electric shock hazard.

In order to more fully understand the method of preparing the body portion 11 of the electroluminescent lamp of this invention, the following procedure is given, but it is to be understood that it is intended to be illustrative only and not to limit the scope of the invention.

The glass cylinder 13 has two tabs of glass frit containing silver or other metal applied at one end and opposite each other, and the glass tube is heated to substantially its softening point to fire the glass frit on the glass thereby forming electrodes 18 and 20. While the glass tube is still hot, a solution of tin compound such as tin tetrachloride is uniformly sprayed on the inner wall to provide a transparent uniform coating of electrically conductive tin oxide. The tin oxide film is then deleted with hydrochloric acid or by other means in the areas surrounding the electrode 20 to provide a break with the film 14 as illustrated in Fig. 3 so that it is in electrical contact with the electrode 19 only. The electrode 20 may also be maintained out of contact with the electrically conducting film 14 by masking the area off while the film is being formed.

Next a dielectric material such as a plasticized nitrocellulose material is prepared which is similar to lacquer and a field-responsive phosphor material is added which may be from about 10% to 50% by volume in the lacquer, much the same as pigment is added to paint. A thin film of the phosphor containing lacquer is then uniformly applied to the inner surface of the cylinder of the electrically conducting film 14 to form the dielectric layer 15. Preferably, a second thin coating of nitrocellulose lacquer which does not contain phosphor is applied over the layer 15 to form a part thereof and smooth off the inner surface so that a more uniform inner electrically conducting layer 16 may be formed thereover. Generally, the thickness of the dielectric layer should not exceed about fifteen thousandths of an inch, and preferably, it should be less than about five thousandths.

The electrically conducting layer 16 may be applied by thermally evaporating a volatilizable metal such as aluminum, silver, copper or gold. In order to apply the film 16, a bell jar 25 or similar enclosure may be utilized having a rod or wire 26 extending through its upper portion and lead wires 27 and 28 communicating therein as illustrated in Fig. 3.

The glass cylinder 13 is centrally disposed in the bell jar and surrounding a filament 29 having small pieces of aluminum 30 in contact therewith and which is electrically heated by a current applied through lead wires 27 and 28. Tongs 31 are connected to the glass cylinder and the wire or rod 26 for providing movement to the cylinder 13 on movement of the rod or wire 26.

In order to deposit the metal film 16, the bell jar is evacuated by removing substantially all of the air through an exhaust tube 32 and current is applied to the filament 29 thereby heating the same in an amount sufficient to evaporate the aluminum 3! As the aluminum volatilizes, the glass cylinder 13 is uniformly drawn upward by lifting the rod 26 until a lower portion of the cylinder 13 surrounds the filament 29 and the atmosphere of evaporated aluminum. If desired, more than one pass may be made to increase the thickness of the vapor deposited aluminum film. Also it is contemplated that the first electrically conducting film 14 may be vapor deposited by this method if desired. When the tube 12 is irregularly shaped, modifications are made in the placement of the filament and movement of the Wire 26 which provide the formation of a uniform film 16.

Before the film 16 is deposited, the area in the vicinity of the electrode 19 is masked off to prevent the film from forming at the electrode 19 so that electrical contact exists between the film 16 and the electrode 20 only. The lead wires 21 and 23 are then soldered to the electrodes 19 and 20, and conventionally attached to the screw type outlet 12.

It is to be understood that the form of the invention disclosed herein is to be taken as the preferred embodiment thereof, and that various changes in the shape, size and arrangement of parts as well as various procedural changes may be resorted to without departing from the spirit of the invention or the scope of the following claim.

I claim:

An electroluminescent lamp comprising, a glass body of generally cylindrical shape and open at one end, a first and second electrode fused to said body, a transparent electrically conducting film on the inner wall of said body in electrical contact with the first of said electrodes and out of electrical contact with the second of said electrodes, a layer of solid dielectric material disposed on the inner wall of said electrically conductive film, said dielectric material having a field-responsive phosphor imbedded therein, an electrically conducting layer of material disposed on the inner surface of said dielectric material in electrical contact with the second of said electrodes and out of electricalcontact with the first of said electrodes, a screw type socket adapted to engage a conventional screw type electrical outlet, and means for electrically connecting said screw type socket to said electrodes.

References Cited in the file of this patent UNITED STATES PATENTS 2,714,683 Jenkins Aug. 2, 1955 

